Gui-Peng Yang

Dimethylsulfoniopropionate biosynthesis in marine bacteria and identification of the key gene in this process

Dimethylsulfoniopropionate (DMSP) is one of the Earths most abundant organosulfur molecules, a signalling molecule1, a key nutrient for marine microorganisms2,3 and the major precursor for gaseous dimethyl sulfide (DMS). DMS, another infochemical in signalling pathways4, is important in global sulfur cycling2 and affects the Earths albedo, and potentially climate, via sulfate aerosol and cloud condensation nuclei production5,6. It was thought that only eukaryotes produce significant amounts of DMSP7–9, but here we demonstrate that many marine heterotrophic bacteria also produce DMSP, probably using the same methionine (Met) transamination pathway as macroalgae and phytoplankton10. We identify the first DMSP synthesis gene in any organism, dsyB, which encodes the key methyltransferase enzyme of this pathway and is a reliable reporter for bacterial DMSP synthesis in marine Alphaproteobacteria. DMSP production and dsyB transcription are upregulated by increased salinity, nitrogen limitation and lower temperatures in our model DMSP-producing bacterium Labrenzia aggregata LZB033. With significant numbers of dsyB homologues in marine metagenomes, we propose that bacteria probably make a significant contribution to oceanic DMSP production. Furthermore, because DMSP production is not solely associated with obligate phototrophs, the process need not be confined to the photic zones of marine environments and, as such, may have been underestimated.

Molecular insight into bacterial cleavage of oceanic dimethylsulfoniopropionate into dimethyl sulfide

Significance DMS is an important participant in the global sulfur and carbon cycles. DMS oxidation products cause the formation of cloud condensation nuclei and hence may influence weather and climate. DMS is produced through the cleavage of dimethylsulfoniopropionate (DMSP) mainly by marine bacterial DMSP lyases. The molecular mechanism of DMSP cleavage to generate DMS remains unclear. In this study, the crystal structure of DddQ, a DMSP lyase, was solved, and detailed biochemical and structural analyses were performed. Our results also provided a foremost insight into the catalytic mechanism of the DMSP cleavage reaction. This study offers a better understanding of how marine bacteria cleave DMSP to generate the climatically important gas DMS. The microbial cleavage of dimethylsulfoniopropionate (DMSP) generates volatile DMS through the action of DMSP lyases and is important in the global sulfur and carbon cycles. When released into the atmosphere from the oceans, DMS is oxidized, forming cloud condensation nuclei that may influence weather and climate. Six different DMSP lyase genes are found in taxonomically diverse microorganisms, and dddQ is among the most abundant in marine metagenomes. Here, we examine the molecular mechanism of DMSP cleavage by the DMSP lyase, DddQ, from Ruegeria lacuscaerulensis ITI_1157. The structures of DddQ bound to an inhibitory molecule 2-(N-morpholino)ethanesulfonic acid and of DddQ inactivated by a Tyr131Ala mutation and bound to DMSP were solved. DddQ adopts a β-barrel fold structure and contains a Zn2+ ion and six highly conserved hydrophilic residues (Tyr120, His123, His125, Glu129, Tyr131, and His163) in the active site. Mutational and biochemical analyses indicate that these hydrophilic residues are essential to catalysis. In particular, Tyr131 undergoes a conformational change during catalysis, acting as a base to initiate the β-elimination reaction in DMSP lysis. Moreover, structural analyses and molecular dynamics simulations indicate that two loops over the substrate-binding pocket of DddQ can alternate between “open” and “closed” states, serving as a gate for DMSP entry. We also propose a molecular mechanism for DMS production through DMSP cleavage. Our study provides important insight into the mechanism involved in the conversion of DMSP into DMS, which should lead to a better understanding of this globally important biogeochemical reaction.

Reactive iron and its buffering capacity towards dissolved sulfide in sediments of Jiaozhou Bay, China.

Reactive iron (Fe) oxides in marine sediments play a critical role in removal of free sulfide. In this study, 0.5 and 6 N HCl-extractable Fe, acid volatile sulfide (AVS), and pyrite were examined in sediments at three sites of eutrophic Jiaozhou Bay to investigate the interactions of sulfur and Fe and possible influences of eutrophication on free sulfide removal. The results indicate that formation and accumulation of AVS and pyrite are limited by low availability of labile organic matter, despite eutrophication of the bay water. Quick buffering of free sulfide proceeded mainly via consumption of 0.5 N HCl-extractable Fe (labile Fe), however, the consumption did not result in a depletion of the Fe pool. High residual buffering capacity enables a quick removal of free sulfide in porewater, and thereby it is difficult for sulfide to accumulate and to cause detrimental effects on benthic organisms at the present steady state. Significant effects of eutrophication on Fe and sulfur geochemistry is restricted only to the estuarine sediments which were subject to direct wastewater discharges, whereas no such effects were observed in other sediments of the bay.

Sorption behavior of nonylphenol on marine sediments: Effect of temperature, medium, sediment organic carbon and surfactant

The sorption behavior of nonylphenol (NP, a toxic endocrine disruptor) on marine sediments was studied in detail through a series of kinetic and thermodynamic sorption experiments. The results showed that the sorption reaction of NP on marine sediments reached equilibrium in 1.5 h and that it accorded well with the non-linear Ho-McKay pseudo-second-order model. The sorption isotherms of NP on H2O-treated sediments could be well described by the Linear isotherm model, while the sorption isotherm on H2O2-treated sediments could be well fitted with the Freundlich isotherm model. A positive correlation was found between the distribution coefficient (Kd) and the sediment organic carbon contents. The medium salinity showed a positive relation with the Kd and a negative relation with the dissolved organic carbon (DOC). Hexadecyl trimethyl ammonium bromide (CTAB) enhanced the sorption amount of NP the most, while sodium dodecylbenzenesulfonate (SDBS) enhanced it the least. The sorption reaction of NP on marine sediments was a spontaneous, physical, exothermic and entropy-decreasing process.

Spatial variation of biogenic sulfur in the south Yellow Sea and the East China Sea during summer and its contribution to atmospheric sulfate aerosol

Spatial distributions of biogenic sulfur compounds including dimethylsulfide (DMS), dissolved and particulate dimethylsulfoniopropionate (DMSPd and DMSPp) were investigated in the South Yellow Sea (SYS) and the East China Sea (ECS) in July 2011. The concentrations of DMS and DMSPp were significantly correlated with the levels of chlorophyll a in the surface water. Simultaneously, relatively high ratio values of DMSP/chlorophyll a and DMS/chlorophyll a occurred in the areas where the phytoplankton community was dominated by dinoflagellates. The DMSPp and chlorophyll a size-fractionation showed that larger nanoplankton (5-20 μm) was the most important producer of DMSPp in the study area. The vertical profiles of DMS and DMSP were characterized by a maximum at the upper layer and the bottom concentrations were also relatively higher compared with the overlying layer of the bottom. In addition, a positive linear correlation was observed between dissolved dimethylsulfoxide (DMSOd) and DMS concentrations in the surface waters. The sea-to-air fluxes of DMS in the study area were estimated to be from 0.03 to 102.35 μmol m(-2) d(-1) with a mean of 16.73 μmol m(-2) d(-1) and the contribution of biogenic non-sea-salt SO4(2-) (nss-SO4(2-)) to the measured total nss-SO4(2-) in the atmospheric aerosol over the study area varied from 1.42% to 30.98%, with an average of 8.2%.

Distributions and sea-to-air fluxes of volatile halocarbons in the East China Sea in early winter.

The concentrations of six volatile halogenated organic compounds (VHOC)-chloroform (CHCl(3)), trichloroethylene (C(2)HCl(3)), tetrachloroethylene (C(2)Cl(4)), carbon tetrachloride (CCl(4)), methylchloroform (CH(3)CCl(3)), and bromoform (CHBr(3)) in the East China Sea (ECS) in November and December 2010 were measured by a purge and trap system coupled to a gas chromatograph with an electron capture detection (ECD). Mean (range) concentrations of CHCl(3), C(2)HCl(3), C(2)Cl(4), CH(3)CCl(3), CCl(4) and CHBr(3) in the surface water were 16.90 (0.40-62.92), 16.27 (2.78-83.33), 2.40 (0.39-9.33), 32.29 (19.72-57.68), 1.70 (0.39-8.73) and 17.11 (4.33-34.46) pM, respectively. With the exception of C(2)HCl(3), the concentrations of other five kinds of VHOC generally exhibited a decreasing trend with distance from the coast, with the low values found in the open sea. The anthropogenic sources contributed to the elevated levels of CCl(4) and CH(3)CCl(3), whereas a combination of the anthropogenic and biogenic sources might be responsible for the elevated levels of CHCl(3), C(2)HCl(3), C(2)Cl(4) and CHBr(3). In the depth profiles, vertical distributions of the six VHOC in the water column were complicated, with the maxima occurring at 0-100 m depths. The mean sea-to-air fluxes of CHCl(3), C(2)HCl(3), C(2)Cl(4) and CHBr(3) were estimated to be 21.08, 29.94, 2.05 and 35.50 nmol m(-2) d(-1), respectively, indicating that the ECS was a source for the four VHOC in the atmosphere.

Study on the sorption behaviors of Tween-80 on marine sediments

Batch experiment was carried out to study the sorption behavior of polysorbate 80 (Tween-80) on marine sediments collected from three different sites in Bohai Sea, China. The sorption of Tween-80 reached equilibrium within 3h and the sorption kinetic curve could be divided into two sections: the rapid sorption part and the slow sorption part. The initial sorption rate increased with the organic carbon (OC) content of the sediment. For the sediments treated by HCl and H(2)O, sorption behaviors of Tween-80 fit the linear model very well (R(2): 0.9516-0.9862) at 298K. The sorption occurred primarily due to partition function of the hydrophobic chains of Tween-80 into the organic carbon of the sediments. Sorption of Tween-80 on H(2)O(2)-treated sediments followed the Freundlich model (R(2): 0.9565-0.9732), which indicated that the surface function of clay minerals and other inorganic solids in the sediment played a key role. Moreover, the dependence of sorption on salinity and temperature was examined and the thermodynamic parameters were evaluated. It was found that the sorption was favorably influenced by the increasing salinity and decreasing temperature of seawater. The changes of Gibbs free energy (DeltaG(theta)=-15.33 approximately -17.54 kJ mol(-1)), enthalpy (DeltaH(theta)=-62.23 kJ mol(-1)) and entropy (DeltaS(theta)=-151.68 J mol(-1)K(-1)) of the sorption were also determined. The negative DeltaG(theta) and DeltaH(theta) values indicated that the sorption process was spontaneous and exothermic. The negative DeltaS(theta) value suggested that the degree of freedom decreased during the sorption process.

Sorption of heavy oil onto Jiaozhou Bay sediment

The sorption of heavy oil onto sediment collected from Jiaozhou Bay was studied in a series of kinetic and equilibrium experiments using NaCl solutions. The effects of temperature, salinity, and pH of the medium on sorption behavior were investigated. Sorption equilibrium of the heavy oil and sediment was established within 60 min. The process was shown to follow a pseudo-second-order kinetic rate model. The sorption rate decreased with increasing initial heavy oil concentration in the solution. Batch equilibrium experiments showed that the sorption isotherm could be described by the Freundlich model. The standard free energy change and enthalpy change at the temperatures studied (283, 288, 293, and 298 K) were negative. These findings indicated that the process was spontaneous and exothermic. Salinity, pH and temperature influenced sorption performance. Sorption was favored by higher concentrations of NaCl, by lower pH values and by lower temperatures.

Occurrence, distribution, and ecological risks of phthalate esters in the seawater and sediment of Changjiang River Estuary and its adjacent area

A total of 133 seawater samples and 17 sediment samples were collected from 81 sampling sites in the Changjiang River Estuary and its adjacent area and were analyzed for 16 phthalate esters (PAEs). The Σ16 PAE concentrations in the seawater and sediment samples ranged from 180.3ng·L-1 to 3421ng·L-1 and from 0.48μg·g-1 to 29.94μg·g-1dry weight (dw), respectively, with mean values of 943.6ng·L-1 and 12.88μg·g-1. The distribution of ∑16PAE concentrations in the water column showed that PAE concentrations in the bottom samples were higher than those in the surface samples (except the transect C located inside the Changjiang River Estuary), with the maxima appearing in the bottom layer at the offshore stations. Among the 16 PAEs, di (2-ethylhexyl) phthalate (DEHP), diisobutyl phthalate (DiBP), and dibutyl phthalate (DnBP) dominated the PAEs, with 25.1%, 21.1%, and 18.9% of the Σ16PAEs in seawater, respectively. The comparison of ∑16PAEs and salinities in transects C and A6 suggested that the Changjiang River runoff was an important driving factor influencing the distribution of PAEs. DEHP concentrations in water samples and DEHP and DnBP concentrations in sediment samples exceeded the environmental risk levels (ERL), indicating their potential hazard to the ocean environment.

Spatio-temporal variations of sea surface halocarbon concentrations and fluxes from southern Yellow Sea

Temporal and spatial distributions of five volatile halogenated organic compounds (VHOC), including chloroform (CHCl3), trichloroethylene (C2HCl3), bromodichloromethane (CHBrCl2), chlorodibromomethane (CHBr2Cl), and bromoform (CHBr3), were determined in the southern Yellow Sea (SYS) during four cruises from July 2008 to May 2009. The five VHOC distributed in the study area were affected by river inputs, anthropogenic activities, circulation system, and biological processes. In this study, CHCl3, CHBrCl2, CHBr2Cl, and CHBr3 concentrations showed significant differences between summer 2008 and spring 2009. The sea-to-air fluxes calculated using the equation of Liss and Merlivat (In: Buat-Menard P (ed) The role of air-sea exchange in geochemical cycling, 1986) indicated that the SYS was a source of CHCl3 and C2HCl3 to the atmosphere during the investigation period.